TMRM stability

Dear friends,
I want to begin titrating TMRM for mitochondrial membrane potential 
estimation for apoptosis assays, and found that the supplied data sheet from 
sigma is very scarce, and mol probes does not give much info either. I did 
find in the net a datasheet that warned that TMRM is very unstable in 
solution and should be used immediately. Measuring such small, micro-g 
amounts for individual experiments is impossible for the normal lab (or 
not???), so how do you use TMRM then? How long does it keep stable "enough" 
in solution? I would be very grateful if anyone with experience with TMRM 
could advice me a little on the matter.

Thanks in advance,

Uriel.

PS:I intend to use DMSO as solvent.